This invention relates to an ignition timing control method for internal combustion engines and, more particularly, to an ignition timing control method through which ignition timing can be accurately controlled even in the event of sudden acceleration or deceleration of the engine.
An example of an ignition timing control method for an internal combustion engine is disclosed in Japanese Patent Publication (Kokoku) No. 54-43649. This known method of controlling ignition timing includes the steps of calculating an advance angle control value before top dead center of the engine crankshaft, which value serves as the ignition timing best suited for the engine operating condition and is based on e.g. the rotational speed of the engine and absolute pressure in the engine intake pipe indicative of engine load, presetting a predetermined crank angle position, which serves as a reference position, indicative of a position advanced by a crank angle the magnitude of which is larger than the calculated advance angle control value, calculating a delay time by applying an angle-time conversion to a crank angle extending from the reference position to a crank angle position indicated by the calculated advance angle control value, and determining an ignition position by counting the delay time from the moment the reference position is sensed.
In this conventional method of controlling ignition timing, control is performed on the assumption that the engine will be rotating at the same velocity during the period of time extending from detection of the engine rotational speed, which is applied in the calculation of the advance angle control value, to the moment an ignition signal is generated. In actuality, however, the rotational speed of the engine is not constant in the above-mentioned time period. Accordingly, in order to control ignition timing accurately so that it will occur at the requisite crank angle position, the moment at which the engine rotational speed is sensed is made as close to the reference position as possible. Furthermore, since accuracy declines when counting is performed for too long, the delay time is made as small as possible.
However, if it were possible to accurately predict a fluctuation in engine rotational speed from engine rotational speeds sensed earlier in successive fashion, then not only would it become possible to achieve more accurate control of ignition timing when the engine is accelerating or decelerating, but ignition timing control also would no longer be adversely affected by a prolonged counting time.